Classified as to origin, there are two different types of impulses arising in air guns and firearms. The first, or "open system" involves those impulses which arise solely from dynamic interactions between the weapon and masses which are irretrievably separated from the weapon in firing and are made independent of it. These masses are the projectile and, in firearms, the powder gas driving it, or, in air weapons, the compressed air. Even translatable mounting of the recoil system can only suppress the impulses for the duration of the backward motion of the recoilable system, since when the system impinges on the buffer or detent which limits the backward motion, it makes itself felt again via the impact. By this time, however, the projectile has long since left the barrel, so that it is no longer susceptible to being deflected by the impact or vibration caused by the stopping of the recoil system.
The second, or "closed system" type of impulse in firearms involves impulses due to dynamic interactions of component parts on the occasion of the firing, but without those component parts separating themselves from or becoming independent of the unit of combined parts. In contrast to a massive, relatively sluggish aggregate of components, a few components which are light, moveable, and driven by forces of the system itself can execute a quickly starting movement cycle which is previously specified. Such moved component parts are, for example, in firearms, the firing pin, and in weapons powered by compressed air, the compression pistons with their respective drive springs. The impulses produced during the action of these components are equal and opposite, thus cancelling each other when the moved parts come to a stop. Thus, the impulse of the firing pin is nullified when the firing pin impacts against the bottom of the cartridge. Likewise, the forward impulse, in the firing direction, of the flung compression piston of a compressed-air weapon and the impulse of its compression spring along with that of the backward-moving recoil system neutralizes itself when the piston impacts against the head of the compression cylinder and comes to a stop.
In compressed-air-powered weapons the impulse of the compression piston and the compression spring is substantially greater than that of the comparatively low-mass projectile and the air driving the projectile. This suggests according to the law of reaction, that the associated oppositely directed impulse of the recoil system is little greater in magnitude than that of the piston and the compression spring combined. Thus, the backward motion of the recoil system lasts in practice exactly as long as the forward motion of the compression piston, assuming that the system has adequate free space to move.
In contrast, for hand firearms, the impulse of the projectile and the powder gas makes up a very high fraction of the total impulse acting on the recoil system. Only a small fraction is attributable to the firing pin and its spring. This is explainable by the higher weight of the projectile and the much higher projectile velocity, on the one hand, and the very low weight of the firing pin compared to the compression cylinder of a compressed-air-powered weapon, on the other.
In the theory of dynamics, the impulse I of a body or its momentum is defined as the product of its mass m and its velocity v: EQU I=m.v (1)
The momentum of a body is changed by the action of an external force F on it for a time interval .DELTA.t. This dynamic property is expressed in the so-called impulse equation: the impulse (of the force) equals the change in the momentum, or, in mathematical notation ##EQU1##
It should be noted that the impulses, forces and velocities entering into this equation are vector quantities, having direction.
From this it can be deduced that for two dynamically interacting bodies the masses are inversely related to the velocity changes and the resultant paths. (Here friction and any deformation are disregarded.) EQU m.sub.1 :m.sub.2 =.DELTA.v.sub.2 :.DELTA.v.sub.1 =.DELTA.s.sub.2 :.DELTA.s.sub.1 ( 3)
This theoretical relation is used for calculating the backward movement distance needed for a system in a weapon, which system is translated upon firing the weapon.
In the above discussion, it was assumed that the line of application of a given impulse from a force passes through the center of mass of the body acted upon. However, this is often not the case in reality with component parts of recoilless weapons, which parts are moved and are subject to being acted upon by forces. At best, this assumption is valid for compression pistons and compression springs in recoilless compressed-air-powered weapons. On the other hand, many firing pins of firearms are asymmetrically shaped, and accordingly are asymmetrically acted on by their springs. The separation of the center of mass from the line of action of the force-impulse is especially pronounced in translatably mounted recoil systems in recoilless weapons.
Nearly always in these systems the firing mechanism and the cocking mechanism or breech handle (i.e., bolt knob) are integrated and either are attached outside to the breech casing or they project outward. These eccentrically disposed working parts increase the mass of the recoil system and thereby decrease its backward motion upon firing, which is entirely desirable. Additionally, they are constantly directly connected to the other working parts of the weapon which are inside the breech casing. This simplifies the overall design and as a rule also provides operating advantages.
In the ideal case, the common line of action of the impulses generated in the firing should pass through the center of mass of the recoil system. However, as a result of the above-mentioned asymmetric disposition of parts of the system with respect to the line of action of the impulse this is not achievable. This gives rise to the major disadvantage that the resultant impulse of the projectile and the propellant means acts on the recoil system at a distance "r" from the center of the mass, and hence a torsional impulse is superimposed on the impulse. During the firing phase, this torsional impulse leads to a turning of the system and thus of the entire weapon, around a transverse axis passing through its center of mass and running in a plane which contains the direction of fire and which is approximately horizontal in the normal use position, whereby said transverse axis is perpendicular to the longitudinal axis of the weapon. This of course has detrimental effects on the exit of the projectile, particularly in view of the fact that the shooter does not always hold the weapon in place with the same force. The consequence is a larger dispersion radius of the grouping (i.e., larger distribution pattern). Thus, with known recoilless small arms which are nonetheless not free of torsional impulses, it is fundamentally impossible to achieve significant reduction in the size of the dispersion pattern by means of a more precise setting of the weapon parts.
Because of this there is need to avoid the occurrence of a torsional impulse in firing, or to keep it from having an effect. This can be achieved by relatively simple means, if one establishes masssymmetry in the translatable recoil system, and dynamically balances the system. In the process, however, it will be necessary to increase the overall weight of the weapon to some extent. This presents major difficulties in the case of sporting arms because such weapons have a prescribed weight limit by regulation which is usually already reached without the employment of these proposed dynamic balance measures. Of course, independently of this consideration, it is desirable for small arms to be as light as possible.
The problem underlying the invention is, in small arms of the type described at the beginning of the above discussion, at least substantially to compensate the torsional impulse originating in firing, without making use of additional weights which would establish symmetry of mass in the recoil system.